fifo-v1: new protocol implementation

Implement fifo-v1 protocol: the capability for clients to explicitly queue wl_surface
commits.

The design of the wl_surface interface defines a double buffer, which is intended to support only
(from the point of view of the client) what is sometimes called the 'mailbox' presentation mode:
each request on a wl_surface operates on an accumulated pending state until a .commit request is
issued, immediately and atomically replacing the wl_surface's current state. This means that only
the state related to the latest .commit request will be latched onto.

fifo-v1 is a protocol that aims to support an important use case, namely the FIFO display
presentation mode, which allows to queue the accumulated pending state until the next latching
deadline occurs.

Signed-off-by: Sergio Gómez <sergio.g.delreal@gmail.com>

include/wlr/types/wlr_fifo_v1.h

@@ -0,0 +1,107 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
+#ifndef WLR_TYPES_WLR_FIFO_V1_H
+#define WLR_TYPES_WLR_FIFO_V1_H
+
+#include <wayland-server-core.h>
+
+#include <wlr/types/wlr_compositor.h>
+#include <wlr/types/wlr_scene.h>
+
+struct wlr_fifo_manager_v1_new_fifo_event {
+	struct wlr_fifo_v1 *fifo;
+};
+
+struct wlr_fifo_manager_v1 {
+	struct wl_global *global;
+	struct wl_display *display;
+
+	struct {
+		struct wl_signal new_fifo; // struct wlr_fifo_manager_v1_new_fifo_event
+
+		/**
+		 * Signals that the fifo manager is being destroyed.
+		 */
+		struct wl_signal destroy;
+	} events;
+
+	struct {
+		struct wl_listener display_destroy;
+	} WLR_PRIVATE;
+};
+
+struct wlr_fifo_v1_state {
+	/*
+	 * This field is used to set the fifo barrier on the surface.
+	 * Set when the client makes a .set_barrier request. */
+	bool set_barrier;
+	/*
+	 * This field is used to lock a commit until the fifo barrier on the surface is cleared.
+	 * Set when the client makes a .wait_barrier request. */
+	bool wait_barrier;
+};
+
+struct wlr_fifo_v1 {
+	struct wlr_fifo_manager_v1 *manager;
+
+	struct wl_resource *resource;
+	struct wlr_addon addon;
+
+	struct wlr_surface *surface;
+	struct wlr_output *output;
+
+	// list of commit requests waiting on the fifo barrier
+	struct wl_list commits; // fifo_commit.link
+
+	// per-commit state used with the wlr_surface_synced mechanism
+	struct wlr_fifo_v1_state current, pending;
+
+	// per-wlr_fifo_v1 instance state
+	bool barrier_set;
+	uint64_t last_output_present_nsec;
+	bool surface_occluded_source_armed;
+
+	struct {
+		/**
+		 * Signals that the fifo object is being destroyed.
+		 */
+		struct wl_signal destroy;
+	} events;
+
+	struct {
+		struct wl_listener surface_client_commit;
+		struct wl_listener surface_commit;
+		struct wl_listener output_present;
+		struct wl_listener output_destroy;
+		struct wl_listener fifo_manager_destroy;
+
+		// used to advance the queue when the surface is occluded
+		struct wl_event_source *surface_occluded_source;
+
+		struct wlr_surface_synced synced;
+	} WLR_PRIVATE;
+
+	struct wl_list link; // wlr_scene.fifo_surfaces
+};
+
+/**
+ * Create the wp_fifo_manager_v1_interface global, which can be used by clients to
+ * queue commits on a wl_surface for presentation.
+ */
+struct wlr_fifo_manager_v1 *wlr_fifo_manager_v1_create(struct wl_display *display,
+	uint32_t version);
+
+/**
+ * Used to set the output to which the fifo will be applied.
+ * If output is NULL, the fifo will be unset for a previously set output.
+ * Returns true on success, false on failure.
+ */
+void wlr_fifo_v1_set_output(struct wlr_fifo_v1 *fifo, struct wlr_output *output);
+
+#endif